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Convertible Subordinated Notes (Details) - USD ($) shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 24, 2018	May 08, 2018	May 07, 2018	Mar. 19, 2014
Debt Instrument [Line Items]
Effect of dilutive securities, Convertible junior subordinated debentures (in shares)	0	1,230
Carrying Values of Liability and Equity Components, Convertible Subordinated Notes
Debt issuance costs	$ (901,000)		$ (955,000)
Carrying value of the liability component	319,261,000		319,108,000
Amortization of Debt Issuance Costs	$ 94,000	$ 208,000
Convertible Subordinated Notes [Member]
Debt Instrument [Line Items]
Stated interest rate percentage	2.75%						2.75%
Carrying Values of Liability and Equity Components, Convertible Subordinated Notes
Convertible subordinated notes, principal amount			6,346,000	$ 22,418,000.16	$ 28,800,000	$ 115,000,000	$ 143,750,000
Unamortized discount of liability component	$ (502,000)		(560,000)
Debt issuance costs	(48,000)		(54,000)
Carrying value of the liability component	5,796,000		5,732,000	$ 6,346,000
Carrying value of the equity component	789,000		$ 789,000
Convertible subordinated notes, fair value	6,800,000
Contractual coupon interest expense	0	988,000
Accretion of discount, convertible subordinated notes	$ 57,000	$ 1,160,000
Effective interest rate percentage	3.15%	11.3199%
Amortization of Debt Issuance Costs	$ 6,000	$ 132,000